fix auto test failure under Windows

migrate all test resources to github

trivial improvements

- replace String.deleteIfExists with kotlin.io.Path.deleteIfExists
- remove unused "dtb.src", use "dtb.*.src" instead

Issue cfig#133: support repack ext4 system_dlkm etc.

Done:
  "unpack" and "pack" tasks are supported for sparse/raw ext4 images
TODO:
  sparse/raw erofs images are not supported yet

dtb: refine 'clear' task of DeviceTreeParser

'clear' task can erase .dtb file now

Issue cfig#109: add test case

Issue cfig#107: accept the new change in dtc 1.6.1

Issue cfig#71: refine dtbo unpack/pack

dtbo unpack:
    save image info
    decompile dtb to dts and yaml dts
    print summary
dtbo pack:
    compile dts to dtb
    print summary
boot v0-v4 pack:
    print summary

use mavenCentral in light of JCenter shutdown

fix build on ubuntu 16.04

fix android-9 branch